IN-VENTO 2018 XV Conference of the Italian Association for Wind Engineering 9-12 September 2018, Napoli, Italy
A critical database for the Strouhal number of bridge decks
Bernardo Nicese1, Claudio Mannini1, Antonino Maria Marra1 and Gianni Bartoli1 1Department of Civil and Environmental Engineering, University of Florence, Italy
Corresponding author: Bernardo Nicese, email@example.com
This paper represents a first step towards a prenormative study on the Strouhal number of bridge decks. The main goal of the work is to identify, where possible, a range of values of this important parameter for the most common typologies of deck cross sections to be used for the preliminary design of bridge structures. With this aim in mind, data available in the literature are critically reviewed, collected and classified.
In the last decades, the construction of slender bridge structures characterized by limited mass per unit length and low frequencies of oscillation has become more and more common. As a consequence, the study of vortex-induced vibration (VIV) of bridge decks due to the wind action is a crucial design issue. In particular, the Strouhal number (St) is a parameter of utmost engineering importance, as it allows the estimation of the VIV critical wind speed.
It is well known that the Strouhal number depends on several factors: geometry of bridge deck cross section, angle of attack of the air flow, incoming flow turbulence characteristics, and Reynolds number. In particular, concerning the cross section geometry, a key role is played by the presence of lateral barriers, screens and other non-structural details. As a result, the estimation of the Strouhal number without specific wind tunnel tests is a complicated task. Indeed, presently the available codes do not allow any accurate enough prediction of this parameter for the preliminary design of bridge structures.
This paper reports a few results of an ongoing prenormative study about the Strouhal number for several typologies of bridge deck cross sections (Fig. 1). As a first step, a large number of data available in the scientific literature have been collected and categorized on the basis of some selected key influencing factors.
A synthetic example of the resulting database is reported in Table 1. Therein, both the results of experiments (either in the wind tunnel or at full scale) and computational fluid dynamics (CFD) calculations can be found. All of the values of the Strouhal number reported are made homogeneous considering the height D of the deck without non-structural details (barriers, screens, etc.) as reference dimension.
From the analysis of the data, an estimation of ranges of values for the Strouhal number for the various bridge deck typologies seems viable. Nevertheless, the need of extending the data collection and of considering additional parameters in the classification is also apparent, in order to make smaller the range of Strouhal number values to consider in a preliminary VIV analysis of bridge decks.
Nicese et al. A critical database for the Strouhal number of bridge decks
Table 1. Strouhal number data for various bridge deck cross sections. B and D denote respectively the width and the height of the bridge deck. The Strouhal numbers have been determined through full-scale tests (FULL), wind tunnel experiments (WT), or numerical simulations (CFD). α is the angle of attack of the air flow (positive nose up).
Cross section Bridge B/D Method α Configuration St Quasi-streamlined
box girder (Fig. 1a)
Storebælt East Bridge (Brusiani et al., 2013; Fradsen et al., 2001) 7.75 FULL - - 0.08-0.15 WT 0° Bare 0.11 CFD 0° Bare 0.14
Single box girder (Fig. 1b)
Storebælt East Bridge approach spans (Larose et al., 2006; Schewe et al., 1998) 3.69 FULL - - 0.22 WT 0° Bare 0.16-0.22 Ikara Bridge (Larose et al., 2006) 5.50 FULL - - 0.20 WT 0° Bare 0.16 Twin-box girder (Fig. 1c) Xihoumen Bridge
(Li et al., 2011) 11.04 FULL - - 0.094-0.107 Stonecutters Bridge
(Larose et al., 2003) 13.63 WT 0° Bare 0.20 General twin-box study
(Laima et al., 2013) 10.28 WT 0° Bare 0.15 General twin-box study
(Matsuda et al., 2001) 10 WT -5° Bare 0.17-0.21 0° Bare 0.20 +3° Bare 0.20-0.22 +5° Bare 0.21-0.24 Trapezoidal box girder with lateral cantilevers
Sunshine Skyway Bridge
(Ricciardelli et al., 2001) 6.73 WT -4° Bare 0.15 Barriers 0.12 0° Bare 0.14 Barriers 0.11 +4° Bare 0.09 Barriers 0.09 CRIACIV section inspired by
Sunshine Skyway Bridge (Mannini et al., 2010) 6.43 WT -5° Bare 0.24 0° Bare 0.21 +5° Bare 0.24 CFD 0° Bare 0.154-0.211 Volgograd Bridge (Corriols et al., 2010) 2.06 CFD 0° Bare 0.133 CFD 0° Barriers 0.116 (a) (b) (c) (d)